KR100229792B1 - Improved image coding system having functions for adaptively determining image coding mode - Google Patents

Abstract

The present invention detects whether a corresponding frame to be encoded is a scene change part, and when the detected image is a scene change part image, removes high frequency components of the input image through filtering, and removes high frequency components regardless of the frame string. The present invention relates to an improved image encoding system having an adaptive encoding mode determining function for performing forced intra mode encoding on a frame. To this end, the present invention relates to an average of pixel values of a corresponding frame to be encoded and to A scene change of the input image is detected based on the short-time statistics of a plurality of frames during a predetermined time period based on the average value. High frequency insensitive to human visual characteristics Removing the minute, and then performs a forced intra-mode encoding.

Description

An Improved Image Coding System with Adaptive Coding Mode Determination

1 is a block diagram of an improved image encoding system having an adaptive encoding mode determination function according to a preferred embodiment of the present invention.

2 is a detailed block diagram of the preprocessing block of FIG.

3 is a view showing a determination region for high frequency component limitation determined as one fixed level for an 8x8 pixel block as an example when the input image is a scene change portion according to the present invention;

4 is a view showing a decision region for limiting high frequency components that is adaptively determined based on the complexity of an 8x8 pixel block as an example when the input image is a scene change portion according to the present invention.

5 is an exemplary diagram for an 8x8 pixel block as an example in accordance with the present invention.

6 is an exemplary view showing a one-dimensional low pass filter coefficient of order 7 as an example according to the present invention.

7 is a diagram illustrating a horizontal filtering process at (0, 4) and a vertical filtering process at (3, 0) as an example according to another exemplary embodiment of the present invention.

8 is an exemplary view showing a 2D lowpass filter coefficient of 3x3 order as an example according to another embodiment of the present invention.

9 is an exemplary diagram illustrating a two-dimensional filtering process at position (3, 3) as an example according to another embodiment of the present invention.

10 is a detailed block diagram of a frame prediction block shown in FIG. 2 according to another embodiment of the present invention.

<Explanation of symbols for main parts of drawing>

100, 180: frame memory 110: preprocessing block

115: switching block 120: subtractor

130: image coding block 140: entropy coding block

150: transmission buffer 160: video decoding block

170: adder 190: current frame prediction block

1110: statistical characteristic calculation block 1120: control block

1130: memory block 1140: frame output block

1141: DCT block 1143: quantization block

1145 frequency selector 1147 dequantization block

1149: IDCT block

The present invention relates to a video encoding system for compression encoding video signals. More particularly, the present invention relates to a video encoding system that detects scene transition of an input video using an average value of a plurality of frame signals during a predetermined time input for compression encoding. An improved image encoding system having an adaptive encoding mode determination function suitable for controlling an encoding mode based on a detection result and adaptively adjusting an amount of bits generated after encoding accordingly.

As is well known in the art, the transmission of discrete video signals can maintain better image quality than analog signals. When a video signal consisting of a series of image "frames" is represented in digital form, a significant amount of data must be transmitted, especially for high quality televisions (aka HDTVs). However, since the usable frequency range of the conventional transmission channel is limited, in order to transmit a large amount of digital data, it is necessary to compress the transmitted data and reduce the amount thereof. Among the various compression methods for compressing data, hybrid coding which combines probabilistic coding with temporal and spatial compression is known to be the most efficient, and these techniques have been proposed by the World Standards Organization for example. It is widely disclosed in the recommendations of MPEG-1 and MPEG-2.

Most hybrid coding techniques use motion compensated DCPM (differential pulse code modulation), two-dimensional DCT (discrete cosine transform), quantization of DCT coefficients, VLC (variable length coding), and the like. The motion compensation DPCM determines a motion of an object between a current frame and a previous frame, and predicts a current frame according to the motion of the object to generate a difference signal representing a difference between the current frame and a predicted value. This can be done for example in Staffan Ericsson's "Fixed and Adaptive Predictors for Hybrid Predictive / Transform Coding", IEEE Transactions on Communication, COM-33, NO.12 (1985, December), or "A motion" by Ninomiy and Ohtsuka. Compensated Interframe Coding Scheme for Television Pictures ", IEEE Transactions on Communication, COM-30, NO.1 (January, 1982).

In general, two-dimensional DCT converts digital image data blocks, such as 8x8 blocks, into DCT conversion coefficients by using or removing spatial redundancy between image data. This technique is described in Chen and Pratt's "Scene Adaptive Coder", IEEE Transactions on Communication, COM-32, NO.3 (March, 1984). The DCT conversion coefficient may be processed through a quantizer, a zigzag scan, a VLC, or the like to effectively reduce (or compress) the amount of data to be transmitted.

More specifically, the motion compensation DPCM predicts the current frame from the previous frame according to the motion of the object estimated between the current frame and the previous frame. The estimated motion may be represented by a two-dimensional motion vector representing the displacement between the previous frame and the current frame.

Typically, there are several approaches to estimating the displacement of an object. These are generally classified into two types, one of which is a block-based motion estimation method using a block matching algorithm and the other is a pixel-by-pixel motion estimation method using a pixel circulation algorithm.

In the motion estimation method for estimating the displacement of an object as described above, the displacement is obtained for all of the pixels using the pixel-based motion estimation method. This method has the advantage of being able to estimate pixel values more accurately and easily handle scale changes (e.g., zooming, a movement perpendicular to the image plane), while a motion vector is obtained for each pixel. Since it is determined, it is impossible to send substantially all the motion vectors to the receiver for a large amount of motion vectors to be issued.

In addition, in block-by-block motion estimation, a block having a predetermined size of the current frame is moved by one pixel in a search range of a previous frame and compared with the corresponding blocks to determine an optimal matching block having a minimum error value. From this, the interframe displacement vector (the degree of block movement between frames) for the entire block is estimated for the current frame to be transmitted. Here, in determining the similarity between two corresponding blocks between the current frame and the previous frame, the average absolute difference, the mean square difference, etc. are mainly used, as is well known in the art.

On the other hand, the image bit stream encoded by the encoding scheme as described above, that is, the encoding scheme such as motion compensation DPCM, two-dimensional DCT, DCT coefficient quantization and VLC (or entropy encoding) is transmitted to the output side of the image encoding system. The next transmission point stored in the buffer is sent to the transmitter for transmission to the remote destination. At this time, the transmission time point here is related to the size (i.e. capacity) and transmission rate of the transmission buffer, and is controlled so that no malfunction (data overflow or data underflow) occurs in the transmission buffer.

More specifically, for example, the amount of bits generated for each frame at the time of encoding is changed due to the scene change of the input image. In view of this, in the image encoding system, the average bit rate may be kept constant. Control of the output buffer. That is, the video encoding system checks the bit generation amount up to the frame currently encoded based on the data fullness state information of the output transmission buffer and adjusts the bit amount to be allocated in the current frame. In other words, in the conventional typical video encoding system, the amount of bits generated in the encoding system is adjusted by controlling the quantization step size (QP) substantially based on the data full state information of the output transmission buffer, that is, if the amount of bits generated before has been large, The bit generation amount is controlled by reducing the bit generation amount by adjusting the step size largely, and in the opposite case, by adjusting the quantization step size small to increase the bit generation amount.

However, as described above, the conventional method of adjusting the bit generation amount by adjusting the quantization step size based on the data fullness state information of the output side transmission buffer is to transmit the video data corresponding to each frame at the same data rate. In the case where the input image to be encoded is a scene change image, that is, an image having low correlation between frames on the time axis, the efficiency is lowered in the encoding process such as motion compensation, thereby increasing the amount of bits generated, thereby increasing the quantization step size. As a result, there is a problem that serious image quality deterioration is caused in the reproduced video.

In addition, the video encoding system described above encodes the frame itself at regular intervals between a plurality of omni-directional or bi-directional predictive frame sequences obtained through motion estimation and compensation, as recommended in the MPEG-1 and 2 standards. When the infrastructure frame is inserted and transmitted, the infrastructure frame is generated at regular intervals regardless of whether or not the video frame input for encoding is a scene change part. Under the control of the system controller, the input image is encoded while the inter mode encoding or the intra mode encoding is constantly switched.

However, as mentioned above, the image frame in the scene change part has a low correlation between frames on the time axis. However, in the case of a frame having low correlation between frames, the efficiency of encoding frames such as motion compensation is poor. have. Therefore, the intra-mode encoding may be more effective than the inter-mode encoding in the frame of the scene change portion having low correlation between the frames, and in consideration of the quantization accompanied with the deterioration of image quality in the reception playback image, If intra coding is performed by removing a portion of a high frequency component that is relatively insensitive to characteristics, more efficient and efficient coding will be possible.

Accordingly, the present invention is to solve the above-described problems of the prior art, and based on the short-time statistics of a plurality of frames for a predetermined time based on the average of the pixel value of the corresponding frame to be encoded and the average value of each frame. An improved image encoding system having an adaptive encoding mode determination function capable of detecting a scene change and performing forced intra mode encoding on a corresponding input frame regardless of a frame string when the input image is an image of a scene change part is detected. There is.

Another object of the present invention is to detect a scene change of the input image based on the short-time statistics of a plurality of frames for a predetermined time based on the average pixel value of the corresponding frame to be encoded and the average value of each frame, and detects the input image Filtering removes high frequency components of the input image when the scene is transitioned, and has an adaptive encoding mode decision function capable of forcibly performing intra mode encoding on input frames from which high frequency components are removed regardless of the frame sequence. The present invention provides a video encoding system.

According to an aspect of the present invention, there is provided an intra encoding mode for performing discrete cosine transform, quantization, and entropy encoding on an input current frame, and the current frame and the current frame and a reconstructed previous frame. An image encoding system comprising encoding means having an inter encoding mode for performing discrete cosine transform, quantization, and entropy encoding on a difference signal between prediction frames obtained through motion estimation and compensation using a frame. A statistical characteristic calculation block for extracting an average MIp value of pixels representing the statistical characteristic for each; A memory block that sequentially stores an average Mp value for each extracted frame for a predetermined time period; Extracting a predicted value for a corresponding frame input by using the average (MIp) values for a plurality of frames corresponding to the stored predetermined time, and between the average (MIp) value and the extracted predicted value for each input frame A prediction error value is calculated, and the average and standard deviation of the prediction error values calculated for each frame are calculated to calculate short-time statistics for the predetermined time, and is more temporal than the frames used for calculating the short-time statistics. A control block for generating a control signal for determining an encoding mode of the current input frame input for encoding based on a comparison result between the statistical characteristics of the current input frame existing later and the calculated short-time statistics; And an adaptive encoding path for adaptively performing the intra mode encoding and the inter mode encoding and a forced intra encoding path only for the intra mode encoding, wherein the short-time statistics provided from the control block and statistical characteristics of the current input frame. And a switching means for providing the current input frame to the encoding means through the forced intra encoding path in response to a switching control signal generated based on a comparison result between the two. Provide a system.

According to another aspect of the present invention, there is provided an intra encoding mode for performing discrete cosine transform, quantization, and entropy encoding on an input current frame, and the current frame, the current frame, and a reconstructed previous frame. A video encoding system comprising encoding means having an inter encoding mode for performing discrete cosine transform, quantization, and entropy encoding on a difference signal between prediction frames obtained through motion estimation and compensation using a frame, which is sequentially input for encoding. A statistical characteristic calculation block for extracting an average MIp value of pixels representing the statistical characteristic for each; A memory block that sequentially stores an average Mp value for each extracted frame for a predetermined time period; Extracting a predicted value for a corresponding frame input by using the average (MIp) values for a plurality of frames corresponding to the stored predetermined time, and between the average (MIp) value and the extracted predicted value for each input frame A prediction error value is calculated, and the average and standard deviation of the prediction error values calculated for each frame are calculated to calculate short-time statistics for the predetermined time, and is more temporal than the frames used for calculating the short-time statistics. A control block for generating a filtering control signal of the current input frame input for encoding based on a comparison result between the statistical characteristics of the current input frame existing later and the calculated short-time statistics; Band limiting means for generating a frame from which a high frequency component is removed by filtering the current input frame input for encoding based on a filter coefficient determined according to the generated filtering control signal and limiting a pass band; And an adaptive encoding path for adaptively performing the intra mode encoding and the inter mode encoding and a forced intra encoding path only for the intra mode encoding, wherein the short-time statistics provided from the control block and statistical characteristics of the current input frame. And a switching means for providing the coding means with a frame signal from which the high frequency component has been removed through the forced intra coding path in response to a switching control signal generated based on a comparison result between the two. An improved image encoding system is provided.

The above and other objects and various advantages of the present invention will become more apparent from the preferred embodiments of the present invention described below with reference to the accompanying drawings by those skilled in the art.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As described above, in the hybrid coding system employing a coding scheme such as motion compensation DPCM, two-dimensional DCT, quantization of DCT coefficients, and VLC (or entropy coding) for efficient coding of a video signal, the frame specified in the MPEG recommendation. When encoding into a column (a frame string into which an intra frame is inserted between a plurality of forward or bidirectional predictive frames at regular intervals), the encoding efficiency is reduced when encoding is performed in the inter mode even though the input image is a scene change part. In view of the above, the present invention employs a technical means to always apply intra mode encoding to a frame regardless of a prescribed frame sequence when an image input for encoding is a scene change part.

In addition, when the input image is a scene change image having a low correlation on the time axis between adjacent frames, the quantization step size may be excessively large due to a large amount of bits, which may cause deterioration in image quality (deterioration in image quality due to quantization error). In the present invention, in consideration of this point, if it is determined that the input image is the scene change part, the band of the input image is adaptively limited for a predetermined time (that is, during the scene change), that is, the filtering technique of the input image By applying the method to remove the high frequency components which are relatively insensitive to the human visual characteristics, the technical means of suppressing the increase in the amount of bits generated after encoding is adopted. This technical means minimizes the quantization error in encoding. By doing so, a more natural playback image can be obtained.

1 shows a block diagram of an improved image encoding system having an adaptive encoding mode determination function according to a preferred embodiment of the present invention. As shown in the figure, the image encoding system of the present invention includes a first frame memory 100, a preprocessing block 110, a first switching block 114, a second switching block 116, a subtractor 120, An image coding block 130, an entropy coding block 140, a transmission buffer 150, an image decoding block 160, an adder 170, a second frame memory 180, and a current frame prediction block 190. .

Referring to FIG. 1, an input current frame signal is stored in the first frame memory 100 on the input side, and the current frame signal stored in the first frame memory 100 is described below through a first switching block L11. Connected to one side input b of 114, it is also provided via line L12 to preprocessing block 110, described in detail later with reference to FIG. Here, the other input c of the first switching block 114 is connected to one output (frame signal output) of the preprocessing block 110 through the line L14, and the switching operation of the first switching block 114 is the line L13. Is performed by the control signal CS1 based on the statistical characteristic calculation of the input frame signal provided from the preprocessing block 110 through. The specific switching operation of the first switching block 114 will be described later in detail.

Meanwhile, the preprocessing block 110 constitutes the most characteristic component in the present invention. The statistical characteristics, through the analysis and investigation of the frame signal provided from the first frame memory 100 through the line L12 according to the present invention, That is, the average value of each input frame signal is calculated, and a predetermined time (for example, 1 second) for a plurality of frames (eg, 30 frames) for which the average MIp (average of pixel values) is calculated for each frame. Determining whether the input video signal is a scene change part based on short-term statistics calculated based on statistical characteristic information during the step. If the input image is the scene change part, the pass band of each input frame signal Limiting, ie, adaptively filtering each frame to adaptively remove high frequency components that are relatively insensitive to human visual characteristics, and then first switching through line L15. Provided at input c of block 114. In this case, the frame signal output from the preprocessing block 110 is not necessarily removed through the filtering and the high frequency component is removed so as to be provided to the input c of the first switching block 114 through the line L15 without removing the high frequency component. In this case, hardware will be simplified compared to the case of performing filtering. Detailed operation of the preprocessing block 110 will be described later in detail with reference to the accompanying drawings.

On the other hand, the first switching block 114 connects an input frame signal connected to the input b to the output e or a filtering connected to the input c based on the switching control signal CS1 on the line L13 provided from the preprocessing block 110. Connect the filtered frame signal (or unfiltered frame signal) to output d. In this case, the line b-a-e of the first switching block 114 is a line for the adaptive intra or inter coding mode, and the line c-a-d is a line only for the intra coding mode according to the present invention, that is, the input line. This is a forced intra coding mode line applied when a video is a scene change part. That is, the first switching block 114 switches the connection of the lines b-a-e or the lines c-a-d based on the control signal CS1 on the line L13.

On the other hand, the frame signal on the line L16 (the input frame signal itself or the one-dimensional filtered frame signal) is sent directly to the image coding block 130 via the output g of the second switching block 116 and the line L17 in the intra mode encoding. Or to the subtractor 120 and the current frame prediction block 190 in inter mode encoding. Here, the second switching block 116 switches the contact points according to control from a system controller, for example, a microprocessor, not shown. In the intra mode encoding, the input f on the line L16 is output through the output g. Connected to line L17, and in inter-mode encoding, input f on line L16 is connected to the input of subtractor 120 through its other output. Therefore, in the image encoding block 130 described later, the current frame signal itself (input frame signal filtered through the preprocessing block 110 or the input frame signal) on the line L17 by using a technique such as DCT or quantization during intra mode encoding. In the inter-mode encoding, the error signal on the line L18 (difference value between the current frame signal on the line L16 and the predicted frame signal on the line L21) may be encoded using a technique such as DCT or quantization. In other words, in the intra mode encoding, the input frame signal itself is encoded (DCT, quantization, entropy encoding, etc.) without using motion estimation and compensation techniques. Since the encoding here is substantially the same as that of the inter mode encoding. In the following description, it is assumed that inter-mode encoding is an example for the purpose of understanding and convenience of explanation.

First, the subtractor 120 performs motion compensated predicted motion on the moving object provided from the current frame prediction block 190 described later through line L21 from the current frame signal provided through line L16 and second switching block 116. Subtract the current frame signal, and as a result the data, i.e., the error signal representing the differential pixel value, is obtained by using discrete cosine transform (DCT) and one of the quantization methods well known in the art through the image coding block 130. It is then encoded into a series of quantized DCT transform coefficients. At this time, the quantization of the error signal in the image encoding block 130 is based on the step size based on the quantization parameter QP determined according to the data fullness state information provided from the output side transmission buffer 150 described later through the line L23. Is adjusted.

In addition, in the image encoding block 130, when the input image is the scene change portion, the filtered input frame signal (or input) on the line L17 provided through c-a-d of the first switching block 116 according to the present invention. The frame signal itself is subjected to coding such as DCT and quantization, that is, forced intra mode coding, considering only correlation on the spatial axis without using motion estimation and compensation techniques.

Next, the quantized DCT transform coefficients on line L19 are sent to entropy coding block 140 and image decoding block 160, respectively. Here, the quantized DCT transform coefficients provided to the entropy coding block 140 are encoded by, for example, a variable length coding scheme, and provided to the transmission buffer 150 at the output side. It is delivered to the transmitter not shown for transmission.

On the other hand, the quantized DCT transform coefficients on the line L19 provided from the image coding block 130 to the image decoding block 160 are converted into a frame signal reconstructed again through inverse quantization and inverse discrete cosine transform, and then added to the next stage. And a reconstructed frame signal from the image decoding block 160 and a predicted current frame signal provided from the current frame prediction block 190 to be described later through the line L21. Generated previous frame signal, and the reconstructed previous frame signal is stored in the second frame memory 180. Therefore, the immediately previous frame signal for every frame encoded through this path is continuously updated, and the reconstructed previous frame signal thus updated is sent to the current frame prediction block 190 described below for motion estimation and compensation. Is provided.

On the other hand, in the current frame prediction block 190, the previous reconstructed using a block matching algorithm based on the current frame signal on the line L16 and the reconstructed previous frame signal on the line L20 provided from the second frame memory 180 described above. Predict the current frame in the unit of a predetermined block (e.g., 16 x 16 or 8 x 8 DCT blocks) in the frame's preset search range (e.g., 32 x 32 or 16 x 16 search range) The predicted current frame signal is generated and provided to the subtractor 120 and the adder 170, respectively.

The current frame prediction block 190 also generates a set of motion vectors for each selected block (16 × 16 or 8 × 8 blocks) on line L22 and provides it to the entropy coding block 140 described above. Here, the sets of motion vectors detected are the most predicted in the predetermined search area (e.g., 32 x 32 or 16 x 16 search range) within the frame before the block (16 x 16 or 8 x 8) block of the current frame. It is the displacement between similar candidate blocks. Accordingly, in the entropy coding block 140 described above, the quantized DCT transform coefficients on the line L19 together with the sets of the motion vectors on the line L22 generate an encoded bit stream by, for example, a variable length coding technique. .

Next, a frame signal or a high frequency component which forms the most characteristic part of the present invention and determines whether or not the input image is a scene change portion and selectively removes a high frequency component of the input image through filtering when the input image is a scene change portion. The operation process in the preprocessing preprocessing block 110 which provides this unremoved frame signal itself as an input frame signal on the line L17 for forced intra mode encoding will be described in detail.

FIG. 2 shows a detailed block diagram of the preprocessing block shown in FIG. As shown in the figure, the preprocessing block 110 of the present invention includes a statistical characteristic calculation block 1110, a control block 1120, a memory block 1130, and a frame output block 1140.

Referring to FIG. 2, the statistical characteristic calculation block 1110 receives an input image on the line L12 and calculates a parameter for determining whether the current image is an image for scene change. The average value MIp of the video signal is used. That is, as an example, when the image currently input is called Ip, the pixel value of the Ip image at the position of (x, y) is Ip (x, y).

Therefore, the average value MIp of each input frame signal is obtained as shown in Equation 1 below.

[Equation 1]

In Equation 1, M and N respectively represent integer and horizontal and vertical directions of the video signal. Then, the parameters thus extracted, that is, the average value MIp of each frame, are provided to the next control block 1120.

The reason for using the average value MIp extracted as described above as the statistical characteristic information to be used for determining whether the scene transition part is the scene change part is that if the input video signal is not the scene change part, (Average) is not significantly different from the previous video signal. On the contrary, if the input video signal is a scene change part, the statistical characteristics of the extracted video signal appear much different from the statistical characteristics of the previous video signal. Therefore, in the present invention, it is determined whether or not to change the scene for the input image by using the temporal change of the statistical characteristic value, this determination will be performed in the control block 1120 described later.

That is, the control block 1120 determines whether the current input image is a scene change part by using the parameters provided from the statistical characteristic calculation block 1110, that is, the average value of each frame. The determination signal is provided to the next frame output block 1140 via the line L14. In other words, in the scene transition part of the video signal, there is not much similarity between the previous video and the current video due to the change in time. As a result, the encoding efficiency decreases during the processing of the encoding system such as motion compensation. As the bits are generated, they are accompanied by a large quantization error in the quantization step (which causes a deterioration in image quality due to a blocking phenomenon in the reconstructed reproduced video on the receiver side). Therefore, the present invention detects the scene change of the input image in order to reduce this phenomenon that occurs during the scene change of the image as described above.

More specifically, in the control block 1120, the statistical characteristics (short-term statistics) for a predetermined time (for example, one second) and the corresponding frame input from the statistical characteristic calculation block 1110 are used to detect the scene change of the input image. A parameter (average value) value is compared to determine whether the scene transition. The process of obtaining such short-time statistics is as follows.

First, a process of obtaining statistical characteristics for a predetermined time on an input image may be performed in various ways. However, in the present invention, a parameter that is currently input from a statistical characteristic of a past predetermined time calculated using a one-dimensional prediction device may be used. Predict the value for Then, an error between the predicted value and the statistical characteristic value of the input frame is calculated, and it is determined whether the current input image is the scene change image based on the predicted error calculated here. For this calculation, the control block 1120 stores the MIp value input every frame in the statistical characteristic calculation block 1110 in the memory block 1130. Here, the one-dimensional prediction process is as follows.

For example, assuming that the variable input at time n-1 is x (n-1) and the output variable is y (n-1), the feedback value is y (n-1) by feeding back the previously output value. ) And the predicted value y (n) and the predicted error value e (n) of x (n) input at time n from the previous input value (x (n-1)) are calculated by the following equation.

[Formula 2]

(In the above formula, p is a constant between 0 and 1, and absolute is an absolute operation. Y (n) and x (n) are values based on the current point of time n. After calculating the output signal of the control block 1120 to calculate the frame, the y (n) value is stored in the memory block 1130 as y (n-1), and the x (n) value is x (n−). 1) If the value is stored in the memory block 1130 and x (n) of the next frame is input, the above equation is calculated using these values.)

In other words, the y (n) value is the predicted value of x (n), which is calculated from the y (n-1) value previously output and the x (n) value previously input. 1120 calculates e (n), i.e., a prediction error, from y (n) (i.e., predicting the current value from a previously generated value) when x (n) is input. From this calculated value, it is determined whether the input image is a scene change part.

On the other hand, in the above [Formula 2] p value can be set according to the cycle or the minimum occurrence interval of the scene change occurs, in the present invention, as an example, it is assumed that the time for 1 second. That is, it is assumed that the scene of the video signal can be continuously generated every 1 second. If the value (p) is set too small, the result is assuming that the video signal continues to be generated at short time intervals, which may not match the characteristics of the actual video signal. Similarly, it does not match the characteristics of the actual video signal. If this time is t, only t seconds of video data is used to obtain the statistics of the video signal. In other words, when [p] in Equation 2 is large (i.e., close to 1), the value multiplied by y (n-1) becomes small, resulting in using only statistics for a short time. Given a small value (ie, a value close to zero), the characteristics of the current frame are predicted by using the image signal characteristics for a long time. Therefore, when the frame rate of the video signal is FR (frame / sec), the time of one frame corresponds to 1 / FR. Therefore, if the time for t seconds is determined, p value can be obtained. This process is calculated by the following equation.

[Equation 3]

(Here, threshold is the criterion for negligible values.)

As an example, if the threshold value is set to 0.01 as the maximum value for multiplying the statistics of video signals before t seconds, the q value is 0.666667 and the p value is calculated as 1-0.215 = 0.785. Accordingly, the control block 1120 calculates a y (n) value using the p value set as described above. At this time, the process of obtaining q value is closely related to the threshold value. This value is multiplied by the image signal characteristic at 31 frames because if the characteristic is used for 1 second, only the characteristic for 30 frames is used. You will understand.

Next, a process of extracting an output value of the control block 1120 using the prediction error e (n) calculated through the above process is as follows.

First, the control block 1120 calculates the prediction error mean Me and the standard deviation Se for a predetermined time by using the prediction error values calculated for each frame as described above. The process of calculating is as follows.

As described above, the statistics of the video signal are the average value of the input video signal, that is, MIp. Using this value, assuming that x (n) of Equation 2 described above, the value of each prediction error value eMIp can be calculated. have. In this case, the application process may be regarded as the average value MIp instead of the input value x (n), and the prediction value may be calculated through each calculation process, and the error value eMIp may be calculated. Then, you can calculate the Me and Se values by using the resulting values to find the mean and standard deviation for one second of this value. That is, when the frame rate of the video signal is 30, 30 average and standard deviation values for the prediction error for 1 second are generated, respectively, and the average and standard deviation of these values are obtained.

Meanwhile, since the prediction error value calculated as described above occurs every frame, when one new prediction error value is calculated, the prediction error value calculated in the past 31st frame is discarded and replaced with the newly calculated prediction error value to the next calculation. I use it. Therefore, for this calculation, the memory block 1130 should store eMIp, which is values of prediction errors calculated by using the MIp value input every frame in the control block 1120, for 1 second.

Therefore, if the value of the prediction error currently calculated in the control block 1120 is eMIp (0), the output signal B in the control block 1120 uses the three statistical values eMIp, Me, Se calculated as described above. It is calculated as follows.

[Equation 4]

Therefore, the output signal B calculated as described above and generated on the line L14 is provided to the frame output block 1140. When the output signal B on the line L14 is 0, MIp (0), which is a characteristic of the video signal currently input, is input. ) Means that it is not a scene change part because there is not much change compared with the previous short time characteristic.In contrast, when the output signal B on the line L14 is 1, the characteristic of the currently input video signal is the previous short time characteristic. Compared with, it means that it is a scene change part because there are many changes. That is, the control block 1120 detects whether or not the average of the pixel value of the current input frame suddenly changes by using the short time statistics obtained from the frame for the previous predetermined time based on the statistical characteristics of each frame, and based on the detection result It is determined whether the current input video is a scene change video.

As a result, in the frame output block 1140, based on the output signal B on the line L14, the current frame signal on the line L12 provided from the first frame memory 100 of FIG. Is generated on the line L15 or a frame signal from which a predetermined high frequency component is removed by performing an appropriate band limiting process, that is, filtering. That is, when filtering the input frame signal on the line L12, in the frame output block 1140, as shown in FIG. 3 as an example, all values below Z (1, 7) and Z (2, 6) are zero. Mapping to (0) value limits the bandwidth and filtering.

The output frame signal from which the high frequency component has been removed is then connected to the forced intra coding mode line L17 via the c-a-d path of the first switching block 114 of FIG. Accordingly, in the image encoding block 130 of FIG. 1, the frame signal on the line L17 from which the high frequency component is relatively insensitive to the human visual characteristics is removed, and the encoding is performed in consideration of the correlation on the spatial axis through a technique such as DCT or quantization. will be.

On the other hand, the frame output block 1140 is switched to provide a frame output on the line L15 only when the input image is a scene change part by switching the frame signal on the line L12 without employing a filtering technique for removing high frequency components of the input frame. In the case of the configuration, the amount of generated data may be slightly increased as compared with employing a filtering technique, but has another advantage of easy hardware implementation. Therefore, it may be applied selectively (or adaptive) according to the application range of the video encoding system to be employed.

On the other hand, in the control block 1120, when the frame output block 1140 described below according to the present invention is configured to filter the input frame signal to generate a frame signal from which high frequency components have been removed, The output signal B may be calculated as shown in the following equation so that the input frame may be filtered adaptively (or selectively) in consideration of the complexity of the input image without filtering the input frame.

[Equation 5]

Therefore, the output signal B calculated as described above and generated on the line L14 is provided to the frame output block 1140. When the output signal B on the line L14 is 1, MIp (0), which is a characteristic of the video signal currently input, is input. ) Means that it is not a scene change part because there is not much change compared with the previous short time characteristic, and when the output signal B on the line L14 is 2, 3, 4, the characteristic of the currently input video signal is Compared with the previous short-time characteristic, it means that it is a scene change part because there is much change. That is, the control block 1120 detects whether or not the average of the pixel value of the current input frame is suddenly changed by using the short time statistics obtained from the frame for the previous predetermined time based on the statistical characteristics of each frame, and based on the detection result. It is determined whether the current input video is a scene change video.

As a result, in the frame output block 1140, on the basis of such an output signal B on the line L14, a corresponding band limiting process corresponding to the current frame signal on the line L12 provided from the first frame memory 100 of FIG. In other words, adaptive filtering is performed. That is, when filtering the input frame signal on the line L12, the frame output block 1140 corresponds to the output signal B from the control block 1120 based on the complexity of the input image, as shown in FIG. 4 as an example. By mapping the value below the output value (that is, the value below the dotted line in FIG. 4) to a zero value, the bandwidth is limited and filtered. In other words, according to the present embodiment, the high frequency component removal level of the input frame signal is selectively (or adaptively) adjusted according to the complexity of the input frame.

Then, the output frame signal from which the high frequency component is adaptively (or selectively) removed as described above is inputted to the forced intra coding mode line L17 via the c-a-d path of the first switching block 114 of FIG. Connected. Accordingly, in the image encoding block 130 of FIG. 1, the correlation of the spatial signal on the spatial axis through DCT, quantization, or the like is applied to the frame signal on the line L17 in which the high frequency component relatively insensitive to the human visual characteristics is selectively or adaptively removed. You will be encoding.

In addition, the control block 1120 sequentially updates the prediction error eMIp values for each frame stored in the memory block 1130 according to the sequential input of the current frame, that is, when eMIp (0) for one new frame is input, The stored value of eMIp (30) is replaced by the value of eMIp (29), the value of eMIp (29) is replaced by the value of eMIp (28), and finally the value of eMIp (1) is converted to the value of eMIp (0). By replacing, it is possible to calculate a newly updated short time statistic for one input image, and this updating process is performed every frame. As a result, the time for which the parameter for each frame extracted by the statistical characteristic calculation block 1110 is stored in the memory block 1130 corresponds to 30 frames, and after 30 frames, the parameter is not used to calculate short-time statistics. As such, the memory block 1130 that stores the parameters of each frame for short-term statistical calculation may be simply configured using, for example, a first-in, first-out buffer.

On the other hand, the control block 1120 in the control block 1120 is a short time statistics for a predetermined time, for example, a second input image for a predetermined time calculated using 30 frames eMIp stored in the memory block 1130 and the statistical characteristic parameters of the current input image ( Based on the determination result when determining whether the current input image is the scene change part based on MIp), the control signal CS1 (eg, high or high) for switching the contact point in the first switching block 114 of FIG. A logic signal having a low level) is generated on the line L13.

In other words, in the control block 1120, when it is determined that the current input image is not the scene change part, as a result of comparing the short-time statistics for a predetermined time with respect to the previous image and the statistical characteristic (MIp) of the current input image, the line L13 phase is displayed. A logic signal of high or low level is generated in the control unit so that b-a-e of the first switching block 114 shown in FIG. 1 is connected. In contrast, when it is determined that the current input image is a scene change part, the line A logic signal of low or high level is generated on L13 to control c-a-d of the first switching block 114 shown in FIG. 1 to be connected. As a result, based on the control signal CS1 on the line L13 provided from the control block 1120, when b-a-e of the first switching block 114 is connected, the current input frame signal itself on the line L11 is adaptive intra / When connected on the line L16 for inter-mode encoding, on the contrary, when c-a-d of the first switching block 114 is connected, the frame signal or the high frequency component on the line L15 provided by the aforementioned frame output block 1140 is removed. Frame signal will be connected on the forced intra mode encoding line L17 according to the present invention.

On the other hand, when the frame output block 1140 is configured to generate a frame signal on which the high frequency component has been removed through filtering the input frame signal on the line L15, the method for removing the high frequency component is one-dimensional. Low pass filtering, 2D low pass filtering, band limiting using Discrete Fourier Transform (hereinafter abbreviated as DFT) and band limiting using Discrete Cosine Transform (abbreviated as DCT) Techniques;

As described above, when a frame from which a high frequency component relatively insensitive to human visual characteristics is removed is provided as an input frame signal on a forced intra coding mode line L17 according to the present invention, among the techniques for removing the high frequency component, One one-dimensional low pass filtering technique is performed by multiplying an input video signal by a low pass filter. That is, when the value of each pixel for an image of one block of N × M (for example, 8 × 8 blocks) is f (x, y), one block is 8 as shown in FIG. 5 as an example. For a block of x8, the position values x and y of the pixels in the horizontal and vertical directions have integer values between 0 and 7, and each value has a level value between 0 and 255. That is, as can be seen from Fig. 5, the position values in the horizontal and vertical directions of each pixel of the 8x8 block have a value of f (0, 0) to f (7, 7).

On the other hand, as the one-dimensional low-pass filter in the present invention, as shown in Figure 6 as an example, it was assumed that the one-dimensional low-pass filter coefficient has seven orders. The low pass filter is an example of a low pass filter that band-limits the signal to have a frequency bandwidth of fs / 4 because the frequency bandwidth is fs / 2 when the sampling frequency of the input video signal is fs.

Therefore, in the frame output block 1140, the process of performing one-dimensional low pass filtering on the image signal according to the present invention performs one-dimensional low pass filtering on each direction since the input image signal is a two-dimensional signal in the horizontal and vertical directions. This can be achieved by This process is illustrated in detail in FIG. 7, which shows a horizontal filtering process at (0, 4) and a vertical filtering process at (3, 0). That is, if the low pass filtered signal in the vertical direction at the position of (x, y) is z (x, y), this is calculated by the following equation.

[Equation 6]

In the above Equation 6, T denotes the order of the filter, and therefore T = 7. Thus, the u and v values have integer values between -3 and 3. In addition, in [Equation 6] above, the k (u) value is a filter coefficient value, and the f (x, y) value is a pixel value. If (y-u) of f (x, y-u) is smaller than 0 in [Equation 5] above, it is set to 0 or larger than M-1 corresponding to the image size of one frame. Let M-1 be the value. This is a method of setting the end value when the pixel value exists only in the area, that is, 0 to M-1, and this filtering method is a technique known in the art.

Therefore, if the filtering is performed at all pixel positions as shown in [Equation 6], as shown in FIG. 7 as an example, one-dimensional filtering in the horizontal and vertical directions can be obtained. In this case, according to the present invention, in the process of performing such filtering at all pixel positions, horizontal filtering may be performed first, and vertical filtering may be performed again or the order of the horizontal filtering may be performed again.

On the other hand, the one-dimensional low pass filtering as described above may be configured to completely remove or partially remove the high frequency components of the input video signal by using only one preset filter coefficient (or fixed). In consideration of this, according to the size of the complexity, a plurality of filter coefficients (for example, four, etc.) may be used to adaptively (or selectively) remove high frequency components of the input image. In this case, when the input frame is adaptively filtered using a plurality of filter coefficients, the hardware implementation may be more complicated than the image filtering using one preset filter coefficient, but the image encoding block 130 of FIG. Another advantage is that in the quantization process, precise control of the quantization step size is possible. Therefore, in the case of adaptive filtering using a plurality of filter coefficients as described above, it may be selectively applied according to its application range.

On the other hand, two-dimensional low-pass filtering among the techniques for the high frequency component removal of the input frame, as shown in Figure 5, is a block of each pixel for a block of N × M, for example, 8 × 8 blocks Assume that the value is f (x, y), and as an example, as shown in Fig. 8, the two-dimensional low pass filter coefficient has a 9th order having 3 orders, as shown in the following formula: It depends on the coefficient k, where the value of k (0, 0) is 1/2 and the other values have a value of 1/16.

Accordingly, the process of performing two-dimensional low pass filtering of the input frame signal on the line L12 in the frame output block 1140 according to the present invention, for example, shows a process of performing filtering at the position of f (3, 3). As shown in. In FIG. 9, the result of the filtering is obtained by adding up the product between the filter coefficient and the overlapping pixels. If the two-dimensional low pass filtered signal at the position of (x, y) is called Z (x, y), this value is calculated by the following equation.

[Formula 7]

In the above formula, T means the order of the filter, so T = 3. Thus, the u value has an integer value between -1 and 1. Also, in the above expression, the k (u, v) value is a filter coefficient value, and the f (x, y) value is a pixel value. In this case, as in the above-described one-dimensional low pass filtering, if the values of (xu) and (yv) of f (xu, yv) are smaller than 0 in the above equation, the value is set to 0, or corresponds to the image size of one frame. If it becomes larger than the M-1 value, the M-1 value is used. Therefore, if the filtering is performed at all pixel positions as in the above equation, as shown in FIG. 9, two-dimensional filtering in the horizontal and vertical directions can be obtained.

On the other hand, when the band limiting technique using the DFT is adopted among the techniques for removing the high frequency components of the input frame, the frame output block 1140 determines the bandwidth for frequency domain division provided to the control block 1120 described above. On the basis of the output signal B, the high frequency component is relatively insensitive to the visual field of the input image. The process can be divided into two-dimensional frequency conversion process and frequency selection process. In this case, the discrete Fourier transform process is performed. (DFT), and in the frequency selection process, the passband of the DFT-converted video signal is determined based on the output signal B provided from the control block 1120.

Next, the frame output block 1140 performs a two-dimensional DFT conversion on the input frame on the line L12 and selects a frequency of the two-dimensional DFT-converted video signal based on the output signal B for bandwidth determination. Explain.

First, the frame output block 1140 uses the similarity of the spatial region of the input image signal. The frame output block 1140 uses the Fourier function to convert the image signal (pixel data) of the spatial region according to the following equation. For example, two-dimensional DFT transform coefficients in a frequency domain of 8x8 units are converted.

Equation 8

In the above formula, f (u, v) denotes the value of each pixel, u denotes the position in the horizontal direction, and v denotes the position of the pixel in the vertical direction. Therefore, the value for each pixel of the N × N block has the following value. That is, when N = 8 u and v have a value between 0 and 7. At this time, each value has an integer value between 0 and 255. In addition, in the above formula, Z (k, 1) means the converted signal, k, 1 means the frequency component in the horizontal and vertical direction, respectively. Therefore, when N = 8, an 8x8 DFT block, that is, a signal in the spatial domain is converted into a signal in the frequency domain.

More specifically, in the frame output block 1140, the DFT conversion coefficients obtained through the above-described process are passed based on the output signal B for bandwidth determination provided from the control block 1120 through the line L14. Determine the frequency band to be In this case, as shown in Equation 5, the output signal B for bandwidth determination may be set to an integer value between 1 and 4, and the selected frequency is as follows.

That is, the frame output block 1140 selects a specific frequency from the converted frequency Z (k, 1). Here, k and 1 are integer values between 0 and N-1. Therefore, the value output from the frame output block 1140 becomes a signal from which a specific frequency component (ie, a high frequency component) is removed. For example, in the case of N = 8, as shown in FIG. 4 as an example, the pass frequency band will be determined.

Accordingly, as shown in FIG. 4, the frequencies below the dotted line corresponding to each of the frequencies are all zero according to the output signal B for determining the bandwidth provided from the control block 1120 to the frame output block 1140 through the line L14. Do not choose. That is, when the B value is 4 in FIG. 4, frequencies below the dotted line such as Z (1, 7), Z (2, 6), etc. are all mapped to 0. FIG. Alternatively, a single predetermined filter coefficient may be used to limit high frequency components of a predetermined level or more (replace high frequency components of a fixed level or more with 0, etc.) in response to the output signal B from the control block 1120. In this case, the implementation will be somewhat easier than the adaptive (or optional) band limitation.

Next, as described above, the DFT transform coefficients (signals in the frequency domain) from which the frequency (high frequency component) of the specific region is removed according to the output signal B value for bandwidth determination determined based on the complexity of the image are expressed as follows. The inverse is transformed into the original spatial signal.

[Equation 9]

In the above formula, f (u, v) means the value of each pixel, u and v means the position of the pixel in the horizontal and vertical direction, Z (k, 1) means the converted signal, k 1 denotes frequency components in the horizontal and vertical directions, respectively. Therefore, when N = 8, 8 x 8 DFT blocks in the frequency domain are converted into signals in the spatial domain (pixel data).

As a result, in the frame output block 1140, when the input image is the scene change portion on the line L15, the bandwidth calculated based on the complexity of the input image, that is, the image signal from which the frequency of a specific region is selectively removed according to the complexity of the image. According to the output signal B for the determination, a frame signal in which the high frequency component of the image is selectively (or adaptively) removed (an image signal in which the high frequency component of a specific region is replaced with a value of 0) is generated. The frame signal in which the high frequency component, which is relatively insensitive to the visual characteristics of the frame, has been selectively removed) is obtained by using the image coding block (c-a-d line of the first switching block 114 of FIG. 1 and the forced intra coding mode line L17). 130).

On the other hand, when the band limiting technique using DCT is adopted among the techniques for removing high frequency components of the input frame, the frame output block 1140 determines the bandwidth for frequency domain division provided to the control block 1120 described above. Based on the output signal B to limit the high frequency components which are relatively insensitive to the time of the input image, the process can be substantially divided into two-dimensional frequency conversion process and frequency selection process, in which the discrete cosine transform is performed in the two-dimensional frequency conversion process. (DCT), and in the frequency selection process, the pass band of the DCT-converted video signal is determined based on the output signal B provided from the control block 1120.

Next, in the frame output block 1140, the process of selecting the frequency of the 2D DCT transformed video signal based on the 2D DCT transformed input signal and the output signal B for determining the bandwidth for frequency domain division. A detailed description will be given with reference to the accompanying drawings.

First, the frame output block 1140 performs 2D DCT conversion on the input image. As is well known in the art, the DCT conversion process is known to reflect the spatial similarity of the image signal. The technique is widely applied in the process of encoding a video signal, and thus, detailed description thereof is omitted here. Therefore, in the present embodiment, when the input image is a scene change part, DCT transform having such characteristics (reflecting spatial similarity) is used as an effective frequency selection technique according to the complexity of the image signal. Such a frequency selection process according to the present invention returns to the frequency domain by better reflecting the characteristics of the image signal than the simple frequency converter method, and as a result, the efficiency can be increased when selecting the frequency for the input image.

FIG. 10 shows a detailed block diagram of the frame output block 1140 according to the present invention shown in FIG. As shown in the figure, the frame output block 1140 includes a DCT block 1141, a quantization block 1143, a frequency selector 1145, an inverse quantization block 1147, and an IDCT block 1149.

In Fig. 10, the DCT block 1141 uses the similarity of the spatial domain of the video signal. The DCT block 1141 uses the cosine function to convert the video signal (pixel data) of the spatial domain using a cosine function, e.g. For example, two-dimensional DCT transform coefficients of a frequency domain of 8x8 units are converted and provided to the next quantization block 1143.

Equation 10

In the above equation, F (u, v) means the converted DCT coefficient, and f (x, y) means the input video signal. Here, x and y denote positions in the horizontal and vertical directions of the pixel data, and u and v denote frequencies in the horizontal and vertical directions in the converted DCT coefficients. The quantization block 1143 then quantizes the two-dimensional transformed DCT coefficients using the above-described equation, for example, using a nonlinear operation to a finite number of values. In this case, the QP value is used in the quantization process of the DCT transform coefficient. When the transformed DCT coefficient is F (u, v), an operation of performing an integer value by performing F (u, v) / (2 * QP) is performed. This is an example of a representative quantization process.

Meanwhile, the frequency selector 1145 uses the output signal B for bandwidth determination provided from the control block 1120 of FIG. 2 through the line L14 for the DCT transform coefficients quantized through the above-described process. Determine the frequency passed. In this case, as shown in Equation 5, the output signal B for bandwidth determination may be set to an integer value between 1 and 4, and the selected frequency is as follows.

That is, the frequency selector 1145 selects a specific frequency from the converted frequency Z (k, 1). Here, k and 1 are integer values between 0 and N-1. Therefore, the value output from the frequency selector 1145 becomes a signal from which a specific frequency component (ie, a high frequency component) is removed. For example, if N = 8, its pass frequency will be determined as shown in FIG.

Accordingly, as shown in FIG. 4, the frequencies below the dotted line corresponding to each of the frequencies according to the output signal B for determining the bandwidth provided from the control block 1120 to the frequency selector 1145 through the line L14 are all zero. Do not choose. That is, when the B value is 4 in FIG. 4, frequencies below the dotted line such as Z (1, 7), Z (2, 6), etc. are all mapped to 0. FIG. On the contrary, in response to the output signal B from the control block 1120, a single predetermined filter coefficient may be used to limit high frequency components of a predetermined level or more (replace high frequency components of a fixed level or more with 0, etc.). In this case, the implementation may be somewhat easier than the adaptive (or selective) band limitation.

Next, as described above, when the input image is a scene change part, the quantized DCT from which the frequency (high frequency component) of the specific region is removed according to the output signal B value for bandwidth determination determined based on the complexity of the input image. The conversion coefficients are restored to the original signal (pixel data) through the next inverse quantization block 1147 and the IDCT block 1149. At this time, the inverse transformation process of the inverse quantized DCT transformation coefficient in the IDCT block 1149 is as shown in the following equation.

[Equation 11]

In the above equation, f (x, y) means inversely transformed video signal (pixel data), and F (u, v) means transformed DCT coefficient. Here, u and v denote horizontal and vertical frequencies in the converted DCT coefficients, and x and y denote horizontal and vertical positions of the pixel data.

As a result, in the IDCT block 1149, when the input image is the scene change portion on the line L15, the bandwidth is calculated based on the complexity of the input image, that is, the image signal from which the frequency of a specific region is selectively removed according to the complexity of the image. Generates a frame signal (video signal in which a high frequency component of a specific region is replaced with a value of 0) by selectively (or adaptively) removing high frequency components of an image according to the output signal B for The frame signal in which the high frequency component relatively insensitive to the visual characteristic is selectively removed) is obtained by the image coding block 130 via the c-a-d line and the forced intra coding mode line L17 of the first switching block 114 of FIG. Will be provided.

Accordingly, in the image encoding block 130 of FIG. 1, the preprocessing block 110 in the image encoding system according to the present invention uses a filtering technique for removing high frequency components (band using one-dimensional or two-dimensional low pass filtering, DFT, or DCT). (Restriction), if the input image is a complicated scene change part, the frame signal itself or the frame from which the high frequency component is removed through the forced intra coding mode line L17 connected to the output d of the first switching block 114 is removed. Forcible intra-mode coding such as DCT and quantization taking into account the correlation on the spatial axis is performed on the signal (the signal from which the high frequency component relatively insensitive to human visual characteristics) is removed. Efficient coding of images as well as low quantization error for low frequency signals It can be done.

As described above, according to the present invention, the short-term statistics of a plurality of frames for a predetermined time and the statistical characteristics of the currently input video frame are used for the input video input to the video encoding system for encoding the desired bit rate. It is determined whether the video inputted for current encoding is a complex scene change part. If the input image is a complex scene change part, the high frequency component insensitive to the human visual characteristics using the corresponding frame signal itself or a filtering technique is determined. Enforced intra mode encoding such as DCT and quantization is performed on the frame signal from which the sine is removed so that coding efficiency can be achieved through forced intra mode encoding that does not use motion estimation even when a scene change situation having a large complexity occurs in the input image. Can not only improve The amount of bits generated after coding without increasing the excessive quantization step size of the quantization step can be effectively controlled and,

Therefore, according to the present invention, it is possible to effectively suppress deterioration in image quality due to quantization error inevitably occurring in a reproduced image when reconstructing and displaying the encoded image on the receiving side.

Claims (14)

Intra-coding mode for performing discrete cosine transform, quantization, and entropy encoding on an input current frame, and a differential signal between the current frame and a prediction frame obtained through motion estimation and compensation using the current frame and a reconstructed previous frame. An image encoding system comprising encoding means having an inter encoding mode for performing discrete cosine transform, quantization, and entropy encoding for a pixel, comprising: an average Mp of pixels representing a statistical property for each frame sequentially input for encoding A statistical characteristic calculation block for extracting a value; A memory block that sequentially stores an average value for each of the extracted frames for a predetermined time period; Extracts a predicted value for a corresponding frame input using MIP values for a plurality of frames corresponding to the stored predetermined time, and for each input frame, between the MIP value and the extracted predicted value. A prediction error value is calculated, and the average and standard deviation of the prediction error values calculated for each frame are calculated to calculate short-time statistics for the predetermined time period, and the temporal time is higher than the frames used for calculating the short-time statistics. A control block for generating a control signal for determining an encoding mode of the current input frame input for encoding based on a comparison result between the statistical characteristics of the current input frame existing later and the calculated short-time statistics; And an adaptive encoding path for adaptively performing the intra mode encoding and the inter mode encoding and a forced intra encoding path only for the intra mode encoding, wherein the short-time statistics provided from the control block and statistical characteristics of the current input frame. And a switching means for providing the current input frame to the encoding means through the forced intra encoding path in response to a switching control signal generated based on a comparison result between the two. system. The method of claim 1, wherein the plurality of frames during the predetermined time period is the previous 30 frames immediately adjacent in time to the frame input for the encoding. Video encoding system. Intra-coding mode for performing discrete cosine transform, quantization, and entropy encoding on an input current frame, and a differential signal between the current frame and a prediction frame obtained through motion estimation and compensation using the current frame and a reconstructed previous frame An image encoding system comprising encoding means having an inter encoding mode for performing discrete cosine transform, quantization, and entropy encoding for a pixel, comprising: an average Mp of pixels representing a statistical property for each frame sequentially input for encoding A statistical characteristic calculation block for extracting a value; A memory block that sequentially stores an average value for each of the extracted frames for a predetermined time period; Extracts a predicted value for a corresponding frame input using MIP values for a plurality of frames corresponding to the stored predetermined time, and for each input frame, between the MIP value and the extracted predicted value. A prediction error value is calculated, and the average and standard deviation of the prediction error values calculated for each frame are calculated to calculate short-time statistics for the predetermined time, and is more temporal than the frames used for calculating the short-time statistics. A control block for generating a filtering control signal of the current input frame input for encoding based on a comparison result between the statistical characteristics of the current input frame existing later and the calculated short-time statistics; Band limiting means for generating a frame from which a high frequency component is removed by filtering the current input frame input for encoding based on a filter coefficient determined according to the generated filtering control signal and limiting a pass band thereof; And an adaptive encoding path for adaptively performing the intra mode encoding and the inter mode encoding and a forced intra encoding path only for the intra mode encoding, wherein the short-time statistics provided from the control block and statistical characteristics of the current input frame. And a switching means for providing the coding means with a frame signal from which the high frequency component has been removed through the forced intra coding path in response to a switching control signal generated based on a comparison result between the two. Improved Image Coding System. 4. The improved encoding method as claimed in claim 3, wherein the plurality of frames during the predetermined time period is the previous 30 frames immediately adjacent in time to the frame input for the encoding. Video encoding system. The method of claim 3, wherein the band limiting means selectively removes the high frequency component level of the current input frame through one-dimensional low pass filtering using one of a plurality of filter coefficients having different values. An improved image encoding system having an adaptive encoding mode determination function. 6. The improved method of claim 5, wherein the one-dimensional low pass filtering is performed sequentially in the horizontal-vertical or vertical-horizontal direction of each pixel position in the 8x8 block. Video encoding system. 4. The improved video encoding system of claim 3, wherein the band limiting means removes high frequency components of the current input frame through two-dimensional low pass filtering. 8. The adaptive encoding mode determination according to claim 7, wherein the band limiting means selectively removes the high frequency component level of the current input frame by using one of a plurality of filter coefficients having different values. An improved video encoding system with functionality. 4. The method of claim 3, wherein the band limiting means converts the video signal in the spatial domain for the current input frame into DFT transform coefficients in the frequency domain in M × N block units by using Discrete Fourier Transform. Determine a high frequency pass band for the converted DFT transform coefficient blocks based on a filtering control signal for band limitation, limit the high pass band of each converted DFT transform coefficient block to the determined bandwidth, And a frame signal from which the high frequency component is removed by reconstructing the original signal through an inverse discrete Fourier transform for each limited DFT block. The bandwidth limitation of the current input frame is adaptively performed at any one of a plurality of preset levels according to the complexity of the input frame. . 12. The adaptive encoding mode of claim 9 or 10, wherein the bandwidth limit maps a high frequency component below the determined bandwidth to zero values for each of the transformed DFT transform coefficient blocks. Improved picture coding system with decision function. 4. The method of claim 3, wherein the band limiting means comprises: a discrete cosine for converting an image signal in a spatial domain with respect to the current input frame signal into a two-dimensional DCT transform coefficients in a frequency domain in M × N block units using a cosine function. Conversion means; Quantization means for quantizing the 2D DCT transform coefficient blocks in M × N units using a quantization parameter value to a finite number of values; A frequency for determining a high frequency pass band for the quantized DCT transform coefficient blocks based on the filtering control signal provided from the control block, and limiting a high frequency pass band of each of the quantized DCT transform coefficient blocks to the determined bandwidth Selection means; And performing inverse quantization and inverse discrete cosine transform on each of the bandwidth-limited quantized DCT blocks to reconstruct the original signal before encoding to generate a band-limited frame, wherein the band-limited frame is removed from the high frequency component. An improved image encoding system having an adaptive encoding mode determination function, characterized in that it is made up of image reconstruction means provided to said switching means as a signal. 13. The adaptive encoding mode determination function of claim 12, wherein the bandwidth limitation of the current input frame is adaptively performed at any one of a plurality of preset levels corresponding to the complexity of the input frame. An improved image encoding system with 14. The adaptive encoding mode according to claim 12 or 13, wherein the bandwidth limit maps high frequency components below the determined bandwidth to zero values for each of the transformed DCT transform coefficient blocks. Improved picture coding system with decision function.